Canoe

I am too cheap to invest in a rack system and I hate the idea of screwing into the roof. And quite frankly unsure what I would be screwing into to do it. 2 screws into an aluminum roof doesn't make me feel comfortable about the rack getting ripped off with air turbulence. I assume there must be wood along the edges where the factory roof carriers attach but unsure. The foam blocks just seem like it would put too much pressure on a small area. My roof seems to be soft to the touch on the front and back edges...maybe it is soft from rot but it appears to be solid just normal movement of the roof material.
Was thinking of a t bar set up off of the front and back and hover over the roof.